swc-project/swc · error

cap == 0

Error message

cap == 0

What it means

CachingResolver::new asserts its cache capacity is non-zero before building the LruCache (which requires NonZeroUsize). This fires when a caller constructs a CachingResolver with cap == 0, i.e. a zero-sized cache, which the LRU implementation cannot represent; the default constructor uses 40.

Source

Thrown at crates/swc_ecma_loader/src/resolvers/lru.rs:35

}

impl<R> Default for CachingResolver<R>
where
    R: Resolve + Default,
{
    fn default() -> Self {
        Self::new(40, Default::default())
    }
}

impl<R> CachingResolver<R>
where
    R: Resolve,
{
    pub fn new(cap: usize, inner: R) -> Self {
        Self {
            cache: Mutex::new(LruCache::new(
                NonZeroUsize::try_from(cap).expect("cap == 0"),
            )),
            inner,
        }
    }
}

impl<R> Resolve for CachingResolver<R>
where
    R: Resolve,
{
    fn resolve(&self, base: &FileName, src: &str) -> Result<Resolution, Error> {
        {
            let mut lock = self.cache.lock();
            //
            if let Some(v) = lock.get(&(base.clone(), src.to_string())) {
                return Ok(v.clone());
            }
        }

View on GitHub (pinned to 5176682b65)

Solutions

1. Pass a capacity of at least 1 to CachingResolver::new
2. Use CachingResolver::default() when no specific capacity is needed (defaults to 40)
3. If zero caching is desired, use the inner resolver directly instead of the caching wrapper

When it happens

Trigger: Thrown at crates/swc_ecma_loader/src/resolvers/lru.rs:35 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of swc-project/swc@5176682b65 (2026-08-17). Data as JSON: /api/errors/3f5eec0822c26f27. Report an issue: GitHub.